The invention relates to an electromotive furniture drive for a piece of furniture. The invention also relates to a method for monitoring a pulse-width ratio of an electromotive furniture drive. The invention also relates to a corresponding piece of furniture.
Furniture with several supporting surfaces for supporting a person situated on the piece of furniture is widely known and used as beds, sofas, chairs and the like. These pieces of furniture comprise at least one movable supporting surface which is movably mounted relative to at least one further supporting surface. The movable supporting surface is a backrest part and/or a leg part which is adjustable by means of at least one electromotive furniture drive. For this purpose, the movable supporting surface can be pivotable, displaceable or both by means of a suitable fitting. It is also possible that a base element such as a bed frame is arranged in a height-adjustable fashion with one or several furniture drives.
An electromotive furniture drive comprises at least one electric motor, which is frequently arranged as a commutator DC motor. The motor is provided downstream with a gear, wherein usually a DC gear motor is used. The electromotive furniture drive further comprises an operating unit and a control unit. The operating unit can be arranged in a wire-bound or wireless manner and comprise a number of pushbuttons, which upon actuation supply via signal transmission a control signal for electrically triggering the respective motor in the respective direction of rotation.
Various solutions have been provided for positioning an output element of the electromotive furniture drive. In one of these solutions, the control unit comprises a counter for counting pulse signals of a respective motor. The pulses are added in a first direction of rotation, and subtracted in a second direction of rotation. So-called memory control units are used for the repeated setting of a previously determinable position. The previously determinable position can be stored by the user and repeatedly retrieved again (i.e. set again).
Motors with Hall sensors, reed contacts and light barriers as pulse generators are known. Hall sensors are expensive and difficult to mount, e.g. their signal generators (magnets) are complex to mount separately from the Hall sensors which are arranged on separate circuit boards. Two Hall sensors are required for the reliable recognition of the direction of rotation. Cabling with multi-core cables (e.g. five-core motor cable) is necessary. The control unit requires the use of a microprocessor or microcomputer. Existing furniture without a memory control unit cannot be retrofitted or only with difficulty.
The document DE 10 2009 049 267 A1 describes a method and an apparatus for positioning an output element of an electromotive drive, especially for a piece of furniture. In this process, the pulses of a back-EMF of a respective electric motor are detected and evaluated.